I have learned that what one focuses their attention on will eventually manifest

That opening statement of yours is not entirely accurate.

In fact, you could write the exact opposite statement and it will be equally accurate :)

I have learned that what one does not focus their attention on will eventually manifest

The paradox can be reconciled by understanding that you do not create through your ongoing focus...you only allow the creation. So your focus on your goal at all is irrelevant to the actual creation of it. For a full explanation, see What should we imagine, visualize or believe?

The only value then in focusing at all on what you want (because you'll get it whether or not you focus) is for the enjoyment of the focus.

If you are not enjoying the focusing on the end-result, you might as well not bother focusing on it at all and let what you want come to you by itself while you focus elsewhere instead on something you do enjoy focusing on.

Ask any genuine creative artist what they truly enjoy about their art and they will tell you that is the creative process that draws them to it, not the materialistic end result of the music, painting, sculpture, movie etc.

The same applies to our physical lives for we are the creative artists of our own physical realities. It is the creative process that makes our lives enjoyable, not the end result of the physical manifestation.

The true value of the physical manifestation is as an excuse to enjoy the process of manifesting it.

Actually both of you are right. You will both experience exactly what you are conscious of. So one of you thinks focusing will lead to manifestation (: hold focus and it will :). The other says if you focus on something it blocks the manifestation (: that will also be the experience :). You experience what you are conscious of because you can only be conscious of what you are conscious of in essence.

Now, having said that. A baseline or foundation of emotional well-being is required for all pleasant desires to flow from us into their manifestation in our reflection (: conditions :). If you're focusing and it is a strain then it is best to switch to something (: anything :) that you do feel good about. When you persist in focus in an EFFORT to "make things happen" what you're doing is holding both the pleasant and unpleasant desire in your consciousness and attempting to mold the unpleasant into the pleasant. This will usually result in more of being "stuck2. You don't mold or change the unpleasant into the pleasant or v.v. - they are different states of mind altogether you just pick one to "occupy" via focus / imagination. So it really is smart to imagine for the pleasure of imagining and, indeed all the "manifestation" is entirely about the feeling achieved (: nobody would deliberately seek to manifest a Bentley if it meant constant unhappiness :).

You cannot actually "surrender your attachment", you just switch your attention to something else and that is why multiple interests are desirable or learn to be emotionally indifferent to the manifestation (: meditation helps a lot here :). The best way to focus your attention would be to develop your connection with your eternal state of GENERAL well-being and enjoy and appreciate as much as you can of the journey to the manifestations (: which are only temporary stops really :).

What you do is let go of the thought after the manifestation session. If it pops up, simply tell yourself that it's coming AND GET BUSY DOING SOMETHING ELSE THAT WILL TAKE YOUR ATTENTION OFF THE MATTER. This is the hardest part of the process to learn. If you're bored and not engaged in something, it's too easy to keep thinking about it, and that is a way to express doubts.

If your manifestation requires your participation (I'm writing a book, so mine does), then you need to stay present. For example: Write for writing's sake. Write for the book's sake. Write to improve your writing. Write because it's fun watching ideas come forth and take shape. Write because you enjoy learning. Don't write because you are manifesting a book.

PS: I've never tried manifesting this type of thing before, but I've been manifesting for many years, and this seems to be following the same route that I used when I wanted to learn how to play the piano - and play it well. I practiced for the joy of learning, I endured the scales because I quickly realized why I needed to be so good at them. I practiced for the reward of getting better, and for the amazement as I watched my abilities flower. In my manifesting sessions, I saw myself playing the grand piano that I had already manifested. I was playing a Chopin Nocturne, I can now play that Nocturne. Not bad, considering where I began.